/*********************************************************************
 MODULE NAME:    b64.c

 AUTHOR:         Bob Trower 08/04/01

 PROJECT:        Crypt Data Packaging

 COPYRIGHT:      Copyright (c) Trantor Standard Systems Inc., 2001

 NOTE:           This source code may be used as you wish, subject to
 the MIT license.  See the LICENCE section below.

 DESCRIPTION:
 This little utility implements the Base64
 Content-Transfer-Encoding standard described in
 RFC1113 (http://www.faqs.org/rfcs/rfc1113.html).

 This is the coding scheme used by MIME to allow
 binary data to be transferred by SMTP mail.

 Groups of 3 bytes from a binary stream are coded as
 groups of 4 bytes in a text stream.

 The input stream is 'padded' with zeros to create
 an input that is an even multiple of 3.

 A special character ('=') is used to denote padding so
 that the stream can be decoded back to its exact size.

 Encoded output is formatted in lines which should
 be a maximum of 72 characters to conform to the
 specification.  This program defaults to 72 characters,
 but will allow more or less through the use of a
 switch.  The program enforces a minimum line size
 of 4 characters.

 Example encoding:

 The stream 'ABCD' is 32 bits long.  It is mapped as
 follows:

 ABCD

 A (65)     B (66)     C (67)     D (68)   (None) (None)
 01000001   01000010   01000011   01000100

 16 (Q)  20 (U)  9 (J)   3 (D)    17 (R) 0 (A)  NA (=) NA (=)
 010000  010100  001001  000011   010001 000000 000000 000000


 QUJDRA==

 Decoding is the process in reverse.  A 'decode' lookup
 table has been created to avoid string scans.

 DESIGN GOALS:	Specifically:
 Code is a stand-alone utility to perform base64
 encoding/decoding. It should be genuinely useful
 when the need arises and it meets a need that is
 likely to occur for some users.
 Code acts as sample code to show the author's
 design and coding style.

 Generally:
 This program is designed to survive:
 Everything you need is in a single source file.
 It compiles cleanly using a vanilla ANSI C compiler.
 It does its job correctly with a minimum of fuss.
 The code is not overly clever, not overly simplistic
 and not overly verbose.
 Access is 'cut and paste' from a web page.
 Terms of use are reasonable.

 VALIDATION:     Non-trivial code is never without errors.  This
 file likely has some problems, since it has only
 been tested by the author.  It is expected with most
 source code that there is a period of 'burn-in' when
 problems are identified and corrected.  That being
 said, it is possible to have 'reasonably correct'
 code by following a regime of unit test that covers
 the most likely cases and regression testing prior
 to release.  This has been done with this code and
 it has a good probability of performing as expected.

 Unit Test Cases:

 case 0:empty file:
 CASE0.DAT  ->  ->
 (Zero length target file created
 on both encode and decode.)

 case 1:One input character:
 CASE1.DAT A -> QQ== -> A

 case 2:Two input characters:
 CASE2.DAT AB -> QUJD -> AB

 case 3:Three input characters:
 CASE3.DAT ABC -> QUJD -> ABC

 case 4:Four input characters:
 case4.dat ABCD -> QUJDRA== -> ABCD

 case 5:All chars from 0 to ff, linesize set to 50:

 AAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaGxwdHh8gISIj
 JCUmJygpKissLS4vMDEyMzQ1Njc4OTo7PD0+P0BBQkNERUZH
 SElKS0xNTk9QUVJTVFVWV1hZWltcXV5fYGFiY2RlZmdoaWpr
 bG1ub3BxcnN0dXZ3eHl6e3x9fn+AgYKDhIWGh4iJiouMjY6P
 kJGSk5SVlpeYmZqbnJ2en6ChoqOkpaanqKmqq6ytrq+wsbKz
 tLW2t7i5uru8vb6/wMHCw8TFxsfIycrLzM3Oz9DR0tPU1dbX
 2Nna29zd3t/g4eLj5OXm5+jp6uvs7e7v8PHy8/T19vf4+fr7
 /P3+/w==

 case 6:Mime Block from e-mail:
 (Data same as test case 5)

 case 7: Large files:
 Tested 28 MB file in/out.

 case 8: Random Binary Integrity:
 This binary program (b64.exe) was encoded to base64,
 back to binary and then executed.

 case 9 Stress:
 All files in a working directory encoded/decoded
 and compared with file comparison utility to
 ensure that multiple runs do not cause problems
 such as exhausting file handles, tmp storage, etc.

 -------------

 Syntax, operation and failure:
 All options/switches tested.  Performs as
 expected.

 case 10:
 No Args -- Shows Usage Screen
 Return Code 1 (Invalid Syntax)
 case 11:
 One Arg (invalid) -- Shows Usage Screen
 Return Code 1 (Invalid Syntax)
 case 12:
 One Arg Help (-?) -- Shows detailed Usage Screen.
 Return Code 0 (Success -- help request is valid).
 case 13:
 One Arg Help (-h) -- Shows detailed Usage Screen.
 Return Code 0 (Success -- help request is valid).
 case 14:
 One Arg (valid) -- Uses stdin/stdout (filter)
 Return Code 0 (Sucess)
 case 15:
 Two Args (invalid file) -- shows system error.
 Return Code 2 (File Error)
 case 16:
 Encode non-existent file -- shows system error.
 Return Code 2 (File Error)
 case 17:
 Out of disk space -- shows system error.
 Return Code 3 (File I/O Error)

 -------------

 Compile/Regression test:
 gcc compiled binary under Cygwin
 Microsoft Visual Studio under Windows 2000
 Microsoft Version 6.0 C under Windows 2000

 DEPENDENCIES:   None

 LICENCE:        Copyright (c) 2001 Bob Trower, Trantor Standard Systems Inc.

 Permission is hereby granted, free of charge, to any person
 obtaining a copy of this software and associated
 documentation files (the "Software"), to deal in the
 Software without restriction, including without limitation
 the rights to use, copy, modify, merge, publish, distribute,
 sublicense, and/or sell copies of the Software, and to
 permit persons to whom the Software is furnished to do so,
 subject to the following conditions:

 The above copyright notice and this permission notice shall
 be included in all copies or substantial portions of the
 Software.

 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
 KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS
 OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

 VERSION HISTORY:
 Bob Trower 08/04/01 -- Create Version 0.00.00B

 \******************************************************************* */

static const char
		cd64[] =
				"|$$$}rstuvwxyz{$$$$$$$>?@ABCDEFGHIJKLMNOPQRSTUVW$$$$$$XYZ[\\]^_`abcdefghijklmnopq";

/*
 ** decodeblock
 **
 ** decode 4 '6-bit' characters into 3 8-bit binary bytes
 */
void decodeblock(unsigned char in[4], unsigned char out[3]) {
	out[0] = (unsigned char) (in[0] << 2 | in[1] >> 4);
	out[1] = (unsigned char) (in[1] << 4 | in[2] >> 2);
	out[2] = (unsigned char) (((in[2] << 6) & 0xc0) | in[3]);
}

/*
 ** decode
 **
 ** decode a base64 encoded stream discarding padding, line breaks and noise
 */
void decode(char *infile, char *outfile) {
	unsigned char in[4], out[3], v;
	int i, len;
	int j = 0, k = 0;

	while (infile[j]) {
		for (len = 0, i = 0; i < 4 && infile[j]; i++) {
			v = 0;
			while (infile[j] && v == 0) {
				v = (unsigned char) infile[j++];
				v = (unsigned char) ((v < 43 || v > 122) ? 0 : cd64[v - 43]);
				if (v) {
					v = (unsigned char) ((v == '$') ? 0 : v - 61);
				}
			}
			if (infile[j]) {
				len++;
				if (v) {
					in[i] = (unsigned char) (v - 1);
				}
			} else {
				in[i] = 0;
			}
		}
		if (len) {
			decodeblock(in, out);
			for (i = 0; i < len - 1; i++) {
				outfile[k++] = out[i];
			}
		}
	}
}
